Depends on the time of year. In the spring-early fall, Mandalay Bay is a great choice. They have a really nice pool area, including a wave pool and a lazy river. They are a nice mid-range property, with relatively easy access to all the south strip. There's a tram that goes to Excalibur, which has quite a few kid-friendly activities, including a game room and the Tournament of Kings show. We toured the wedding salons there too, so if you were thinking of hosting the wedding there, I can tell you a little about what we saw.
I would not suggest Circus Circus for a wedding trip. It's a very low-budget property, and is pretty unpleasant inside, imo. We found the smell pretty off-putting, and the location is inconvenient as it is past the north end of the strip.
Ew don't stay at Circus Circus. That place makes me want to shower as soon as I step into it. Sorry to the CC fans but yuck!
Pretty much any of the strip hotels are fine for a 2 year old. I've never taken my kids there at that age (I think my son was 7 or 8 the first time), so I'm not a whole lot of help with that. I just made sure that we stayed somewhere that had something other than a casino - mall, food court, great pool, etc. We've stayed at Paris, Planet Hollywood and the Flamingo with the kids.